1. Field of the Invention
The present invention relates to a brake mechanism which includes a piezoelectric element, and to a transport apparatus and industrial apparatus which include the brake mechanism.
2. Description of the Related Art
As a braking device for a conventional vehicle such as an automobile driven by gas, a disk brake has been used, for example. As such a disk brake, pads to be a pair to each other are disposed on both surfaces of a disk which is connected to a tire and rotates along with the tire. When a driver depresses a brake pedal installed at a driver seat, one pad moves toward the other pad by an oil pressure mechanism, for example, and the disk is sandwiched by the pads. Then, a friction force between the pad and the disk decreases a rotation speed of the disk, eventually bringing a rotation of the disk to a halt. A rotation of the tire is also halted by the halt of the rotation of the disk.
In recent years, in order to protect environment, an electric vehicle which has an engine driven by electricity instead of gas has been developed. In order to simplify a structure of the electric vehicle, it is examined to provide a motor instead of providing the oil pressure mechanism thereby to operate the pad by the motor.
Meanwhile, in such an electric vehicle, for safer and comfortable driving, it is examined to make a depressing angle of a brake pedal of the vehicle and a deceleration of a tire correspond closely. For such a purpose, it is required to make the depressing angle of the brake pedal and a pressing force of the pad by the motor corresponded to each other, but adjusting the pressing force with high accuracy by the motor is difficult. Thus, it is examined to provide a piezoelectric element in a rear surface (surface opposite to a pressing surface of the disk) of the pad. More specifically, it is examined to detect a pressure change of a pressure detecting region of the rear surface of the pad by the piezoelectric element and to control an operation of the motor based on a detection result.
However, when the disk is pressed, in some cases, a pressure in a certain point of the pad becomes temporarily large or small compared with a pressure in another point, due to minute irregularities of the pressing surface of the pad and each surface of the disk, for example. Since a variation of the pressure becomes sometimes large as described above, stable control cannot be always done. Though a disk brake of the electric vehicle has been explained here, in a device using a brake mechanism which controls a rotation speed of a disk by pressing the disk as above it is required that braking is performed with high accuracy in correspondence with a user's operation, similarly to in the disk brake.
Patent Document 1 describes, with regard to a pressure sensor constituted by a crystal, a structure in which a plurality of electrodes are formed in one side of a crystal piece, but cannot solve the above-described problem.
(Patent Document)
Japanese Patent Application Laid-open No. 2001-349816